The present invention relates to a vehicle activity measuring apparatus which is located on a road for monitoring road traffic, such as vehicle speed, number of passing vehicles, types of passing vehicles, e.g., small size vehicle, large size vehicle and so forth, and for collecting vehicle activity data.
Conventionally, such a vehicle activity measuring apparatus performs image processing of background image data and current image data taken to show activities of vehicles on the road for measuring passing vehicle speeds, number of the passing vehicles, types of passing vehicles, e.g., small size vehicle, large size vehicle or so forth, and thus output information indicative of results of measurement.
In addition, the apparatus extracts the front end of a particular vehicle and obtains amount of movement of the front end to give the vehicle speed. Namely, the amount of movement of a particular vehicle is derived on the basis of a positional difference between a current position of the front end of the particular vehicle and an immediately preceding position of the front end of the particular vehicle, and the processing time.
However, in the above-mentioned conventional vehicle activity measuring device, when failure of extraction of the particular vehicle is caused during tracing of the vehicle, the device terminates tracing and measurement, and when the same particular vehicle is extracted in a subsequent process, the device starts tracing and measurement for the particular vehicle again as a new particular vehicle. As a result, the data for the single vehicle may be erroneously recorded as data for two vehicles.
Furthermore, when a temporary offset of the extracted front end image of the vehicle relative to the actual front end position occurs, such an offset may instantly affect measurement of the vehicle speed.
On the other hand, the above-mentioned conventional vehicle activity measuring apparatus is set with a measuring area corresponding to one lane, and when the particular vehicle traced by the apparatus changes its running lane from the monitoring lane, the apparatus fails to trace the particular vehicle. In addition, in case that the particular vehicle to be traced is a large size vehicle, it can be detected not only on the running lane but also on the adjacent lane due to its imaging angle causing an erroneous detection.
Additionally, the above-mentioned conventional vehicle activity measuring apparatus is basically designed for performing measurement of a running vehicle and is difficult to detect presence of stopped vehicles, such as those stopped due to heavy traffic in the day time (hereafter, simply referred to as "presence detection").
Furthermore, in the night time, the apparatus performs tracing and measurement of the vehicles by detecting head lights. However, when the vehicles stop in traffic jam, the head lights may be turned off with small lamps on. Presence detection in such circumstances is more difficult.
Also, in the above-mentioned conventional vehicle activity measuring apparatus, tracing and measurement are performed by detecting a pair of head lights in the night time. Erroneous detections may be caused by reflected head lights from a wet road surface during rain.
Furthermore, when light axes of the head lights are in oblique in the field due to the imaging angle, it may become difficult to detect a pair of head lights if the process is performed in a respective scanning. It is particularly difficult to detect small lamps with low luminance stimulating a small number of pixels, which are lit simultaneously with or instead of the head lights.